1. Field of the Invention
The present invention relates to a reactor internal equipment hoisting apparatus for hoisting equipment in a reactor such as dryer, shroud head, etc. installed in a reactor pressure vessel (abbreviated as a "RPV" hereinafter) of a boiling water reactor (abbreviated as a "BWR" hereinafter).
2. Description of the Related Art
A large number of fuel assemblies are loaded in the inside of the RPV of the BWR, and a core consists of these fuel assemblies.
FIG. 7 is a vertical sectional view showing a reactor internal structure of the BWR. As shown in FIG. 7, a core support plate 2 is placed below the core 1 and a number of fuel assemblies (not shown) constituting the core 1 are supported at their bottom ends by the core support plate 2. Also, an upper grid 3 is arranged over the core 1 such that upper portions of the fuel assemblies are supported by the upper grid 3. The core 1 is surrounded by a cylindrical core shroud 4.
A top portion of the core shroud 4 is covered with a shroud head 5 which forms a plenum 5a. A number of standpipes 6 are stood upright on the shroud head 5 and a plurality of steam separators 7 are connected to respective top portions of the standpipes 6. The steam separators 7 perform steam and water separation of the core water which has been converted into a two phase flow when it is heated by the core 1, and then the separated steam is fed to a dryer (not shown).
When the reactor is operated, the pressure and the temperature of the core 1 are increased by virtue of heat generated by fission reaction of the nuclear fuel and internal pressure is applied to the shroud head 5. In addition, when an earthquake happens, tipping loads are applied to the shroud head 5 and the standpipes 6.
In order to support such internal pressure and such tipping loads, the shroud head 5 is tightened against the core shroud 4 by several tens of shroud head bolts 8 and fixed thereto.
FIG. 8A is a top view showing the shroud head 5 of the BWR, FIG. 8B is a side view showing the shroud head 5 of the BWR, and FIG. 8C is a front view showing a hoisting lug 25 of the shroud head 5 of the BWR. As described above, a number of shroud head bolts 8 are provided around the outer peripheral surface of the shroud head 5, the standpipes 6, and the steam separator 7. These shroud head bolts 8 are inserted in fitting holes (not shown) of lower and upper guide rings 20, 21.
Four rods 17 are provided around the outer peripheral surfaces of the shroud head 5, the standpipes 6, and the steam separator 7 at 90 degree interval. Hoisting lugs 25 shown in FIG. 8C are provided to top ends of each of the rods 17. Hoisting holes 26 into which hooks of shroud head hoisting tools (not shown) are hooked to hoist the shroud head 5 from the RPV are formed in the hoisting lugs 25.
FIGS. 8A and 8B show a configuration in which four rods 17 with the hoisting lugs 25 are evenly spaced at intervals at 90 degree, but the arrangement pattern of the hoisting lugs 25 and the rods 17 are not limited to this configuration. For instance, there is a case where the hoisting lugs 25 and the rods 17 may also be arranged according to an arrangement shown in FIG. 9.
When conducting periodic inspections or fuel exchanges of the reactor, first the shroud head bolts 8 are unscrewed by using a long shroud head bolt wrench from the fuel exchanger. Then, the hoisting apparatus which is hoisted by a main hoisting hook of an overhead travailing crane installed on the ceiling of the reactor building is hung down into the RPV, then the shroud head 5 is clamped by the hoisting apparatus, and then the shroud head 5 is lifted from the RPV to be transferred into an equipment storage pool.
In this case, if the wire rope and the hook of the overhead travailing crane are submerged into the core water with radioactivity during the hoisting operation of the shroud head 5, radioactive contamination is spread over the operation floor.
For this reason, when conducting the hoisting operation of the shroud head 5, first a level of the core water in the reactor well should be lowered previously to some extent, then the hoisting apparatus is hung down into the RPV to grasp the shroud head 5.
While keeping a distance between the level of the core water and the hook of the overhead travailing crane appropriately, the shroud head 5 is gradually lifted correspondingly as the level of the core water in the reactor well is risen gradually. On the contrary, when the removed shroud head 5 is fitted into the RPV again, the shroud head 5 is lowered gradually in accordance with the gradual fall of the level of the core water.
However, upon the above removing and fitting operations of the shroud head 5, since the shroud head 5 must be lifted/lowered slowly in accordance with the slow elevating speed of the core water of the reactor well, there has been such a problem that it take a long time to carry out the above operations.
Therefore, in order to reduce times required for the above removing and fitting operations of the shroud head 5, the reactor internal equipment hoisting apparatus shown in FIG. 10 has been proposed. Even when the reactor well is filled with the core water, this hoisting apparatus can handle the shroud head 5 in the core water without immersion of the hook 10 and the wire rope of the overhead traveling crane in the core water.
The hoisting apparatus shown in FIG. 10 has a supporting frame 31 which is hung down from the hook 10 of the overhead traveling crane by using the hoisting wires 30 and the hook box 11. The supporting frame 31 consists of a pair of beams which intersect orthogonally with each other.
An elevating frame 32 which is constructed by coupling a pair of beams to intersect orthogonally with each other is provided below the supporting frame 31. This elevating frame 32 can be vertically moved by an elevating unit 33 with respect to the supporting frame 31.
The elevating unit 33 has four elevation driving rods 34 composed of roller screws. Lower ends of these elevation driving rods 34 are connected to the upper end surface of the elevating frame 32 via connecting shafts 16.
In addition, the elevation driving rods 34 are inserted into gear boxes 35 provided on an upper end surface of the supporting frame 31. The gear boxes 35 are coupled with elevation driving unit 37 via gear driving rods 36 respectively. The elevation driving unit 37 consist of a power motor (not shown) and a worm reducer (not shown).
Cylinders 39 having piston rods 38 are provided to the elevating frame 32 and connector pins 40 are fitted to top ends of the piston rods 38. The connector pins 40 can be releasably inserted into pin insertion holes (not shown), which are formed in positioning members 41, by moving back and forth the piston rods 38 of the cylinders 39.
When equipments such as the shroud head 5, etc. in the reactor are pulled out of the RPV with the use of the hoisting apparatus shown in FIG. 10, the hoisting apparatus is hung down into the RPV by the overhead traveling crane in the state that the reactor well is still filled with the core water. Then, the hoisting apparatus is put onto the reactor internal equipment by operating the overhead traveling crane. At that time, the hook 10 and the wire rope (not shown) of the overhead traveling crane can be prevented from being immersed into the core water by keeping the supporting frame 31 and the elevating frame 32 spaced sufficiently apart.
However, there has been another problem that, since the elevating driving unit 37, gear boxes 35, gear driving rods 36 constituting the elevating unit 33 are large and complicated mechanism, decontamination operations of the hoisting apparatus becomes difficult after using the hoisting apparatus.
Further, there has been still another problem that, since lengths of the elevating drive rods 34 must be set longer than elevation strokes (about 6 m) of the elevating frames 32, a storage area is restricted because of heights of the elevating drive rods 34, otherwise they disturb to move other equipments during periodic inspection.
Furthermore, there has been yet still another problem that, in the event that only the long elevating drive rods 34 are disassembled to store the reactor internal equipment hoisting apparatus, a leveling of four elevating drive rods 34 must be set to reassembling the reactor internal equipment hoisting apparatus again and therefore it takes a long time to set such leveling.